Electronic Properties of Chemically Etched CdTe Thin Films: Role of Te for Back-Contact Formation

2001 ◽  
Vol 668 ◽  
Author(s):  
D. Kraft ◽  
A. Thiβen ◽  
M. Campo ◽  
M. Beerbom ◽  
T. Mayer ◽  
...  
Keyword(s):  
Fermi Level ◽  
Electronic Properties ◽  
Photoelectron Spectroscopy ◽  
Valence Band Maximum ◽  
Ex Situ ◽  
Back Contact ◽  
Experimental Conditions ◽  
Band Bending ◽  
Fermi Level Position ◽  
Contact Formation

ABSTRACTImprovement of electric back contact formation is one of the major issues of the CdTe thin film solar cell research. Chemical etching of CdTe before metallization is accepted to improve contact formation. It is believed that a CdTe/Te contact is formed by this procedure leading to a Fermi level position in the CdTe close to the valence band maximum for low contact resistance. We have studied the electronic properties of chemically etched CdTe surfaces with photoelectron spectroscopy. Etching of the samples was performed in air (“ex-situ“) as well as in an electrochemical setup directly attached to the UHV system (“in-situ“). The formation of a Te layer is clearly shown by (S)XPS. In contrast to previous studies we could not detect the formation of a p-CdTe surface for different experimental conditions. The detected Fermi level position indicates still band bending and hence a blocking Schottky barrier.

Role of Surfaces and Interfaces for the Electronic Properties of Conducting Oxides

2001 ◽  
Vol 666 ◽  
Author(s):  
Andreas Klein
Keyword(s):  
Work Function ◽  
Electronic Properties ◽  
Photoelectron Spectroscopy ◽  
Band Alignment ◽  
Surface Band ◽  
Band Bending ◽  
Conducting Oxides ◽  
Degenerate Semiconductors ◽  
Surfaces And Interfaces

ABSTRACTTransparent conductive oxides (TCOs) are generally considered as degenerate semiconductors doped intrinsically by oxygen vacancies and by intentionally added dopants. For some applications a high work function is required in addition to high conductivity and it is desired to tune both properties independently. To increase the work function, the distance between the Fermi energy and the vacuum level must increase, which can be realized either by electronic surface dipoles or by space charge layers. Photoelectron spectroscopy data of in-situ prepared samples clearly show that highly doped TCOs can show surface band bending of the order of 1 eV. It is further shown that the band alignment at heterointerfaces between TCOs and other materials, which are crucial for many devices, are also affected by such band bending. The origin of the band bending, which seems to be general to all TCOs, depends on TCO thin film and surface processing conditions. The implication of surface band bending on the electronic properties of thin films and interfaces are discussed.

Characterization of immobilized DNA on sulfur-passivated InAs surfaces

2011 ◽  
Vol 1301 ◽  
Author(s):  
EunKyung Cho ◽  
Pae Wu ◽  
Minhaz Ahmed ◽  
April Brown ◽  
T. F. Kuech
Keyword(s):  
Fermi Level ◽  
Photoelectron Spectroscopy ◽  
Areal Density ◽  
Valence Band Maximum ◽  
Xps Spectra ◽  
Ammonium Sulfide ◽  
Functionalized Surfaces ◽  
Sulfur Passivation ◽  
Sulfide Solution

ABSTRACTThe immobilization of DNA on passivated n-type InAs (100) surfaces has been studied using X-ray and ultraviolet photoelectron spectroscopy. The benefits of sulfur passivation using ammonium sulfide solution ((NH4)2S) for DNA immobilization were examined. The XPS/UPS data carried out on non-functionalized and functionalized surfaces demonstrate that the DNA probes reacted with the sulfur-passivated InAs surface. The XPS data in combination with fluorescently-tagged DNA indicate that the sulfur passivation process leads to a higher and more uniform attachment of DNA over the surface compared to non-sulfur-passivated InAs surfaces. The XPS data obtained immediately after sulfur passivation clearly observes In-S bonding, with little or no As-S. In addition, the XPS spectra of As 3d core-levels immediately after sulfur passivation shows that there is a negligible amount of As-Ox, but the peak become considerable after exposure to the aqueous DNA probe solution. The increase in As-Ox is likely due to the presence of non-sulfur bonded As atoms present on the surface. The presence of sulfur on the surface does lead to the high areal density of attached ssDNA. This system forms the basis of a DNA sensing system. While chemically passivating the surface against oxidation and facilitating probe attachment, the changes in Fermi level position were also monitored by UPS. UPS spectra show that the Fermi level of a clean InAs surface is located ~0.6 eV above the valence band maximum. The changes in electronic states induced by sulfur passivation and the pinning of EF are discussed.

Surface Electronic Structure of Nitric-oxide-treated Indium Tin Oxide

2003 ◽  
Vol 796 ◽  
Author(s):  
Hu Jianqiao ◽  
Pan Jisheng ◽  
Furong Zhu ◽  
Gong Hao
Keyword(s):  
Nitric Oxide ◽  
Binding Energy ◽  
Tin Oxide ◽  
Indium Tin Oxide ◽  
Photoelectron Spectroscopy ◽  
Surface Region ◽  
Valence Band Maximum ◽  
Surface Band ◽  
Band Bending ◽  
Surface Electronic Structure

ABSTRACTThe surface electronic properties of the nitric oxide (NO) treated indium tin oxide (ITO) are examined in-situ by a four-point probe and X-ray photoelectron spectroscopy (XPS). The XPS N1s peak emerged at a high binding energy of 404 eV indicating that NO is reactive with ITO. NO adsorption induces an increase of film sheet resistance, arising from an oxygen rich layer near the ITO surface region, with approximately 2.5 nm thick. This implies that the interaction of NO with ITO is occurred around surface region. Valence band maximum measured for NO-absorbed ITO was shifted to the low binding energy side. This is related to the upward surface band bending.

Electronic Structure of δ-Pu and PuCoGa5 from Photoemission and the Mixed Level Model

2003 ◽  
Vol 802 ◽  
Author(s):  
John J. Joyce ◽  
John M. Wills ◽  
Tomasz Durakiewicz ◽  
Elzbieta Guziewicz ◽  
Martin T. Butterfield ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Fermi Level ◽  
Electronic Properties ◽  
Excellent Agreement ◽  
Fermi Energy ◽  
Photoelectron Spectroscopy ◽  
Spectral Intensity ◽  
Δ Phase ◽  
Level Model ◽  
Photoemission Data

ABSTRACTThe electronic structure of δ-phase Pu metal and the Pu-based superconductor PuCoGa5 is explored using photoelectron spectroscopy and a novel theoretical scheme. Excellent agreement between calculation and experiment defines a path forward for understanding electronic structure aspects of Pu-based materials. The photoemission results show two separate regions of 5f electron spectral intensity, one at the Fermi energy and another centered 1.2 eV below the Fermi level. A comparison is made between the photoemission data and five computational schemes for δ-Pu. The results for δ-Pu and PuCoGa5 indicate 5f electron behavior on the threshold between localized and itinerant and a broader framework for understanding the fundamental electronic properties of the Pu 5f levels in general within two configurations, one localized and one itinerant.

Chemical and Electronic Properties of Metal/Sb2Te3/CdTe Contacts for CdTe Thin Film Solar Cells Studied by Photoelectron Spectroscopy

2003 ◽  
Vol 763 ◽  
Author(s):  
D. Kraft ◽  
B. Späth ◽  
A. Thißen ◽  
A. Klein ◽  
W. Jaegermann
Keyword(s):  
Thin Film ◽  
Solar Cells ◽  
Electronic Properties ◽  
Photoelectron Spectroscopy ◽  
Ohmic Contacts ◽  
Surface Region ◽  
Band Alignment ◽  
Thin Film Solar Cells ◽  
Back Contact ◽  
Cdte Thin Film

AbstractFormation of low resistance back contacts in CdTe thin film solar cells has been a research issue for many years. Ohmic contacts to the absorber layer are typically prepared using the diffusion of dopant atoms from the back contact material into the CdTe forming a thin space charge layer that can be easily tunnelled. Stable CdTe solar cells with reasonable back contact characteristics have been prepared using metal/Sb2Te3 layer sequences. In this study the chemical and electronic properties of such layer systems have been investigated using photoelectron spectroscopy. The vacuum deposited Sb2Te3 layers do not react with the CdTe substrate. Band alignment does not indicate the formation of a good back contact. By subsequent deposition of metals a chemical reaction is induced forming metal-tellurides, a metal/Sb-alloy and elemental Sb. Although an Sb diffusion into the CdTe absorber is observed, no increase of p-doping in the surface region is evident.

scholarly journals Effects of graphene/BN encapsulation, surface functionalization and molecular adsorption on the electronic properties of layered InSe: a first-principles study

2018 ◽  
Vol 20 (18) ◽  
pp. 12939-12947 ◽  
Author(s):  
Andrey A. Kistanov ◽  
Yongqing Cai ◽  
Kun Zhou ◽  
Sergey V. Dmitriev ◽  
Yong-Wei Zhang
Keyword(s):  
Fermi Level ◽  
Work Function ◽  
Electronic Properties ◽  
Surface Functionalization ◽  
First Principles ◽  
Molecular Adsorption ◽  
Band Bending ◽  
Fermi Level Pinning ◽  
First Principles Study ◽  
P Type

A proper adoption of the n- or p-type dopants allows for the modulation of the work function, the Fermi level pinning, the band bending, and the photo-adsorbing efficiency near the InSe surface/interface.

CdS and Cd-Free Buffer Layers on Solution Phase Grown Cu2ZnSn(SxSe1- x)4 :Band Alignments and Electronic Structure Determined with Femtosecond Ultraviolet Photoelectron Spectroscopy

2014 ◽  
Vol 1638 ◽  
Author(s):  
Richard Haight ◽  
Aaron Barkhouse ◽  
Wei Wang ◽  
Yu Luo ◽  
Xiaoyan Shao ◽  
...  
Keyword(s):  
Fermi Level ◽  
Photoelectron Spectroscopy ◽  
Solution Phase ◽  
Buffer Layers ◽  
Photoemission Spectroscopy ◽  
Ultraviolet Photoelectron Spectroscopy ◽  
Band Bending ◽  
Pump Probe ◽  
Fermi Level Pinning ◽  
Band Alignments

ABSTRACTThe heterojunctions formed between solution phase grown Cu2ZnSn(SxSe1- x)4 (CZTS,Se) and a number of important buffer materials including CdS, ZnS, ZnO, and In2S3, were studied using femtosecond ultraviolet photoemission spectroscopy (fs-UPS) and photovoltage spectroscopy. With this approach we extract the magnitude and direction of the CZTS,Se band bending, locate the Fermi level within the band gaps of absorber and buffer and measure the absorber/buffer band offsets under flatband conditions. We will also discuss two-color pump/probe experiments in which the band bending in the buffer layer can be independently determined. Finally, studies of the bare CZTS,Se surface will be discussed including our observation of mid-gap Fermi level pinning and its relation to Voc limitations and bulk defects.

Photoemission Investigation of the 2D Electron Gas Created At the InAs(110) Surface

1998 ◽  
Vol 05 (01) ◽  
pp. 235-240 ◽  
Author(s):  
V. Yu Aristov ◽  
G. Le Lay ◽  
P. Soukiassian ◽  
V. M. Zhilin ◽  
G. M. Grehk ◽  
...  
Keyword(s):  
Synchrotron Radiation ◽  
Fermi Level ◽  
Electron Emission ◽  
Photoelectron Spectroscopy ◽  
Electron Gas ◽  
Low Energy ◽  
Two Dimensional ◽  
Dimensional Electron ◽  
Band Bending ◽  
2D Electron Gas

On InAs(110) surfaces a downward band bending (BB) was produced either by cleavage defects or by adsorption of very small amounts of Cs atoms. As a consequence the Fermi level was moved high into the conduction band, resulting in the formation of a two-dimensional electron channel (2D-EC). Electron emission arising from this channel was detected by angle-resolved photoelectron spectroscopy near the [Formula: see text] points of the first and second surface Brillouin zones. We present a detailed investigation of the corresponding photoemission characteristics using tunable low energy synchrotron radiation light. We find in particular that the photoemission intensity depends drastically on the photon energy. This effect is interpreted as resulting from the quantization of the 2D electron gas in the direction normal to the surface; it is directly linked to the electron density sampled (i.e. the depth probed) beneath the top surface.

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